A common error in regards to the exporting the Salesforce reports to Excel is to receive a "file is corrupt and cannot be opened" message. This is a Salesforce problem which is occurring to many user after Microsoft Office updated in 2016. The most easy solution is to work around the problem.
Unblock access in File Properties
1. Open the folder with the downloaded file
2. Right click on the file, select Properties.
3. On the General tab, click Unblock.
4. Click OK.
For more possible solutions please visit this link from Salesforce.